1. Field of the Invention
The invention relates to a thermally-assisted magnetic recording head used in thermally-assisted magnetic recording in which near-field light is applied to lower a coercivity of a magnetic recording medium so as to record information, and to a head gimbals assembly, a head arm assembly, and a magnetic disk unit that are mounted with the thermally-assisted magnetic recording head.
2. Description of Related Art
A magnetic disk unit has been used for writing and reading magnetic information (hereinafter, simply referred to as information). The magnetic disk unit includes, in a housing thereof for example, a magnetic disk in which information is stored, and a magnetic read write head that records information into the magnetic disk and reproduces information stored in the magnetic disk. The magnetic disk is supported by a rotary shaft of a spindle motor, which is fixed to the housing, and rotates around the rotary shaft. On the other hand, the magnetic read write head is formed on a side surface of a magnetic head slider provided on one end of a suspension, and includes a magnetic write element and a magnetic read element that have an air bearing surface (ABS) facing the magnetic disk. In particular, an MR element exhibiting magnetoresistive effect (MR) is generally used as the magnetic read element. The other end of the suspension is attached to an end of an arm pivotally supported by a fixed shaft installed upright in the housing.
When the magnetic disk unit is in a stationary state, namely, when the magnetic disk does not rotate and remains stationary, the magnetic read recording head is not located over the magnetic disk and is pulled off to the outside (unload state). When the magnetic disk unit is in a driven state and the magnetic disk starts to rotate, the magnetic read recording head is changed to a state where the magnetic read recording head is moved to a predetermined position over the magnetic disk together with the suspension (load state). When the number of rotation of the magnetic disk reaches a predetermined number, the magnetic head slider is stabilized in a state of slightly floating over the surface of the magnetic disk due to the balance of positive pressure and negative pressure. Thus, information is accurately recorded and reproduced.
In recent years, along with a progress in higher recording density (higher capacity) of the magnetic disk, improvement in performance of the magnetic read recording head and the magnetic disk has been demanded. The magnetic disk is a discontinuous medium including collected magnetic microparticles, and each magnetic microparticle has a single-domain structure. In the magnetic disk, one recording bit is configured of a plurality of magnetic microparticles. Since the asperity of a boundary between adjacent recording bits needs to be made small in order to increase the recording density, it is necessary to reduce a size of the magnetic microparticles. However, when the magnetic microparticles are made small in size, thermal stability of the magnetization of the magnetic microparticles is disadvantageously lowered with decreasing volume of the magnetic microparticles. To solve this issue, it is effective to increase anisotropy energy of the magnetic microparticle. However, increasing the anisotropy energy of the magnetic microparticle leads to increase in the coercivity of the magnetic disk. As a result, difficulty occurs in the existing magnetic head in that the information recording becomes difficult.
As a method to solve the above-described difficulty, a method referred to as a so-called thermally-assisted magnetic recording has been proposed. In this method, a magnetic recording medium with large coercivity is used, and when information is written, heat is applied together with the magnetic field to a section of the magnetic recording medium where the information is to be written to increase the temperature and lower the coercivity of that section, thereby writing the information. Hereinafter, the magnetic head used in the thermally-assisted magnetic recording is referred to as a thermally-assisted magnetic recording head.
In performing the thermally-assisted magnetic recording, near-field light is generally used for applying heat to a magnetic recording medium. For example, in Japanese Unexamined Patent Application Publication No. 2001-255254 and in Japanese Patent No. 4032689, disclosed is a technology of allowing a frequency of light to coincide with a resonant frequency of plasmons that are generated in a metal, by directly applying light to a plasmon generator in order to generate near-field light. In the method of directly applying light to a plasmon generator, however, the plasmon generator itself overheats and accordingly deforms depending on usage environment or conditions, making it difficult to achieve practical realization.
As a technology capable of avoiding such overheating, Japanese Patent No. 4104584 proposes a thermally-assisted head using surface plasmon polariton coupling. In this technology, light propagating through a waveguide (guided light) is not directly applied to a plasmon generator, but the guided light is coupled to the plasmon generator through evanescent coupling, and surface plasmon polaritons generated on a surface of the plasmon generator are utilized.
The thermally-assisted magnetic recording head that utilizes the surface plasmon polariton suppresses a rise in temperature of the plasmon generator to some extent. However, it was confirmed that, when Au (gold) is used to configure the plasmon generator for example, there are cases where contraction (agglomeration) resulting from heat occurs especially in a section, near the ABS, where a volume is low and where the heat concentrates.
Such agglomeration is considered to be a phenomenon caused by gold configuring the plasmon generator not being in a stabled state such as a bulk state. That is, since gold formed through a plating method, a sputtering method, or the like is low in density, it is considered that a rise in temperature upon operation of the thermally-assisted magnetic recording head increases the density thereof, and a crystalline structure thereof advances toward a stabilized state.
Hence, it is desirable that a heat treatment be performed in advance during manufacturing to stabilize the crystalline structure of a material (such as gold) configuring the plasmon generator.
On the other hand, since the thermally-assisted magnetic recording head is usually provided together with a magnetic read head that includes the MR element, it is desirable that a heat treatment at a temperature that thermally damages operation performance of the MR element be avoided. Therefore, sufficiently stabilizing a crystalline structure of a constituent material of the plasmon generator to sufficiently suppress the agglomeration thereof upon operation is virtually difficult. When such agglomeration occurs, an end section of the plasmon generator is recessed from the ABS and is away from a magnetic recording medium, incurring a decrease in recording performance.
For the foregoing reasons, what is desired is a thermally-assisted magnetic recording head capable of suppressing agglomeration of a plasmon generator upon operation and performing higher-density magnetic recording.